1. Field of the Invention
The present invention relates to a communication apparatus using a multichannel access method.
2. Related Background Art
Hitherto, according to a communication apparatus using a multichannel access method such as a cordless telephone or the like, which speech communication channel is used is decided by searching a free channel when a call is generated or received.
In the conventional apparatus, however, a noise may occur in an intermodulation frequency or a carrier may be erroneously detected on the basis of the existing signal.
Conventionally, in a cordless telephone system comprising a main apparatus which encloses a plurality of extension lines and outside lines and has an exchanging function and cordless telephones connected to the extension lines, such as a speech communication channel which is used by the cordless telephone, a channel which is not used by a master side or a slave side of the cordless telephone is searched for and the searched for and found channel is allocated to be used.
In the conventional apparatus, however, in the case where a plurality of cordless telephones are connected to the main apparatus. Since each pair of the master and slave independently searches a free channel and uses it, there is a time that when the speech communication channel which is used by a plurality of cordless telephones makes a control channel unusable by a radio wave interference. A speech communication channel which is used by another cordless telephone in the system is sensed and it is erroneously judged that the line is busy.
Hitherto, a communication apparatus of the multichannel access method having a control channel, such as a small power cordless telephone or the like, copes with the above problems mainly by a retransmission of the control signal as a countermeasure for collision of the signals on the control channel.
In the conventional apparatus, however, since the countermeasure for collision of the control signals depends on only the retransmission of the control signal, when the retransmission timing coincides with the timing of the control signal, the retransmission control signal also collides.